1. Field of the Invention
The present invention relates generally to proximity sensors and more particularly relates to proximity sensors adapted to sense warm bodies which are located behind a vehicle.
2. Description of the Prior Art
The problem of detecting warm bodies, such as people and animals, in an area behind a vehicle is well established. The problem is especially acute in the field of farm tractors and lawn mowing equipment. Presently, more than 5,000 injuries occur each year as a result of misuse of such equipment. A large percentage of these injuries are inflicted when a tractor is reversing and inadvertently strikes an unseen victim, resulting in impact injuries and lacerations from contact with a spinning mower blade.
Various forms of sensors have been employed in collision avoidance systems for vehicles. Among these systems are radio-based sensors (radar), ultrasonic sensors, laser-based radar and infrared sensors. Of these sensor technologies, passive infrared sensors (PIR) are particularly well suited for applications where it is desirable to discriminate warm bodies from inanimate objects. One type of PIR sensor, which is well known in the art, employs pyro-electric detectors to sense movement of a warm body in the sensors' field of view. Specifically, pyro-electric detectors detect differences between infrared energy emitted by the warm body or target and its background when triggered by the relative movement of at least one member of the set including the target, the pyro-electric detector, the PIR sensor or the vehicle on which the PIR sensor is mounted. Such detectors are commonly used in security systems to detect the presence of an intruder within a protected premise. Another type of PIR sensor utilizes thermocouple or thermopile technology, which senses mere presence of the warm body. PIR sensors have also been used in robotic systems to detect and track people in the vicinity of a mobile robotic system.
Vehicles, such as lawn tractors and the like, typically operate in an open outdoor environment which is subject to various sources of sensor interference. The typical environment may include irrigation sprinkler systems and fences made of conductive material which substantially interfere with the operation of radio-based proximity sensors. The environment may also include thermal "hot spots," such as areas where solar heating occurs on the ground, which interferes with the operation of conventional PIR sensors. Therefore, there remains a need for a back-up proximity sensor system for a vehicle which overcomes the problems associated with devices known in the prior art.